1. Technical Field
The invention relates to hinged belt conveyor systems such as those used to transport bulk particulate material between different elevations. More particularly, the invention relates to such a hinged belt system having spring biased compensating idler rolls for exerting a predetermined vertical pressure on the central troughing portion of the loaded belt flight for compensating for various belt tensions which changes along the path of the belt between its head and tail pulleys and to maintain the area within the belt generally constant regardless of the amount of material on the belt to insure that the conveyed material moves with the conveyor.
2. Background Information
Hinged belts are relatively new in the art for carrying bulk particulate materials such as mineral, ore, coal, grain and the like. Such a belt includes a central troughing portion and a pair of end flaps which close over the particulate material supported in the central troughing portion as the particulate material moves along an inclined and declined paths to prevent the material from flowing or tumbling inside the belt. Flowing or tumbling of the particulate material usually occurs due to gravity or inertial when the belt starts or stops and upon the incline or decline becoming too severe whereby the friction between the particulate material and the belt is insufficient to prevent the material from moving along the belt independent of the belt movement.
Hinged belts are continuous and extend between a head pulley and a tail pulley, one of which is connected to a drive means for driving the belt. The belt typically has a loaded flight in which the troughing portion faces upward for carrying the material from a loading area usually near a tail pulley to an unload area usually near the head pulley. The belt also has an unloaded flight which extends from the head pulley to the tail pulley on the return run and is located beneath the loaded belt flight.
The loaded flight is supported by a plurality of spaced idler roll sets usually consisting of two or three individual rolls pivotally connected together to form a generally V-shaped configuration for supporting the troughing portion of the belt. Top idler rolls also are provided which press downward on the flaps of the belt and ensure that the belt flaps remain closed and to assist in maintaining the material in a fixed relation on the belt without flowing as the belt moves along its inclined or declined paths.
Some examples of prior known hinged belt and conveyor systems are shown in U.S. Pat. Nos. 2,199,935; 2,365,762; 2,839,180; 3,429,422; 3,999,646; 4,402,395; and 4,410,082. Various frame constructions also are provided for adjusting and supporting idler roll sets on the general frame structure of the conveyor belt for both hinged and non-hinged conveyor belts, such as shown in U.S. Pat. Nos. 3,062,360 and 3,105,588, and German Patent No. 36 06 129.
Australian Patent Specification 15,583 discloses an usual non-hinged conveyor belt having a variable trough arrangement in which the supporting idler rolls are mounted by springs to allow the conveyor trough to vary somewhat depending on the load carried thereby. U.S. Pat. Nos. 4,709,806 and 4,760,913 disclose hinged belt conveyor systems of the type with which the present invention is intended to be incorporated therein and show various types of idler troughing roll sets and top idler compensating roll sets on which the present invention is a further improvement.
It has been found that the spring biasing of the idler troughing rolls such as shown in Australian Patent Specification 15,583 and in U.S. Pat. No. 4,760,913, is able to compensate for certain variations in trough loading but is unsuitable for supplying a sufficient spring biasing force upwardly on the central troughing portion of a loaded belt to enable the hinged belt to prevent the material supported thereby from rolling along the belt or from remaining stationary as the belt moves, for certain applications. This flowing or non-movement of the material with the belt becomes a special problem when a relatively steep incline or decline is encountered and also where the material being conveyed is extremely fluid, for example, particulate material containing a large quantity of water resulting in a near slurry formation.
It has been found that the tension within a conveyor belt varies considerably over the length of the belt and becomes particularly greater near the head pulley, and that as the belt tension increases the closure tension force exerted on the bottom of the belt must also increase to ensure that the material moves along with the belt and does not roll backwards or forwards, or as can occur in some situations, remain stationary with the belt sliding past the material. Again, the amount of tension required at the various positions along the belt is dependent upon the particular material being conveyed and its particular coefficient of friction with the surface of the hinged belt, the angle of incline or decline of the belt, the length of the conveyor belt between changes in elevation, the speed at which the belt is moving, size of the belt and driving motor therefore, etc.
Another problem with hinged belt conveyors is that the belts are not loaded uniformly and the belt will normally carry various amounts of material throughout the length of the belt. For example, a substantial load will be placed onto the belt and additional material may not be placed on the belt for several feet or hundreds of feet along the belt, or may be placed in smaller amounts at one location of the belt and increase and decrease considerably throughout the belt length.
Thus, the need exists for a means of supplying a sufficient upward force on the troughing portion of the hinged belt by a compensating idler roll or rolls, and in which this upward force can be varied along the belt length to correspond with the tension in the belt and to compensate for different materials being carried by the belt.
It is readily seen by ordinary engineering calculations that in order to change the biasing force, that is, the amount of tensioning force exerted vertically upward on a troughing portion of a belt by the use of springs mounted on the end mounting brackets of a generally V-shaped idler roller set, such as shown in Australian Patent Specification 15,583, would require an extremely large, expensive and powerful spring at each bracket location to provide any significant increase in the vertical upward force exerted by the compensating rolls. Such a solution would be impractical due to the additional weight and expense of the springs, and in many situations such springs would not be able to provide the required upward force needed to compensate for tension variations in the belt and load conditions of the conveyed material.